Pacemakers are cardiac rhythm management devices that deliver a series of low energy pace pulses timed to assist the heart in producing a contractile rhythm that maintains cardiac pumping efficiency. Pace pulses may be intermittent or continuous, depending on the needs of the patient. There exist a number of categories of pacemaker devices, with various modes for sensing and pacing one or more heart chambers.
Pacing therapy has been used in the treatment of heart failure (HF). Heart failure causes diminished pumping power of the heart, resulting in the inability to deliver enough blood to meet the demand of the body tissues. Heart failure may affect the left side of the heart, right side of the heart or both sides of the heart, and may cause weakness, loss of breath, and build up of fluids in the lungs or in other body tissues. For example, HF may, when deterioration of the muscles of the heart, reduce the heart's contractility or synchronism. The reduced contractility decreases the cardiac output and may result in an increased heart rate and enlargement of the heart. In some cases, HF is caused by unsynchronized contractions of the left and right heart chambers. Particularly when the left or right ventricles are affected, the unsynchronized contraction can significantly decrease the pumping efficiency of the heart.
Pacing therapy to promote synchronization of heart chamber contractions to improve cardiac function is generally referred to as cardiac resynchronization therapy (CRT). Some cardiac pacemakers are capable of delivering CRT by pacing multiple heart chambers, and the pacing pulses are then delivered to the heart chambers in a sequence that cause the heart chambers to contract in synchrony, increasing the pumping power of the heart and delivering more blood to the tissues of the body. In the case of dysynchrony of right and left ventricular contractions, a biventricular pacing therapy may pace one or both ventricles. Bi-atrial pacing or pacing of all four heart chambers may alternatively be used.
In the following is briefly discussed some patent documents related to optimization of the performance of the heart by use of implantable heart stimulators, and specifically related to CRT.
US-2007/0060961 discloses a method for determining optimal implantation site of an implantable medical lead. Electrical energy is delivered at different sites of the left ventricle to initiate cardiac activation at a plurality of different test locations. A hemodynamic sensor, such as a pressure sensor or blood volume measuring sensor, is used for determining a respective hemodynamic response for the different test sites.
US-2008/177344 relates to the selection of optimal pacing site for CRT with an implantable LV multi-electrode lead. At each of the multiple electrodes in connection with the left ventricle a time parameter equal to the start of a QRS deflection and the peak of the QRS deflection of the LV electrogram is determined.
This time parameter is related to the increase in peak rate of increase of LV pressure. The time parameter should be as large as possible for optimal pacing site with the CRT.
More in detail, in US-2008/177344 the electrode site selection is preferably based on timing interval measurements associated with ventricular depolarization. These timing measurements may be used to identify and/or select electrode site(s) that provide for improved responsiveness to cardiac resynchronization therapy. Electrode sites may be evaluated to identify those that will respond to CRT (“responder sites”), and such identified responder sites may be further evaluated to determine their relative degree of responsiveness to CRT. Responder sites may be characterized by late activation of depolarization and/or prolonged depolarization. Electrode site characterization may be implemented through analysis of a timing interval defined between a first deflection and a maximum deflection of a ventricular depolarization for a given electrode site.
US-2004/0102812 relates to a cardiac rhythm management device adapted to select optimal pacing site for resynchronization therapy. The site selection is based on the relative depolarization times at the sensing/pacing electrode sites during a cardiac contraction. The objective of the therapy is to produce a more coordinated contraction than naturally occurs. This is achieved by selecting the paced site that becomes depolarized later than the other available pacing sites.
Earlier Cardiac Resynchronization Therapy (CRT) systems have only had one lead with two electrodes implanted on the left heart side via the coronary sinus, which means that the pacing vector is limited in flexibility. Even with the newly developed multi (e.g. quadruple) pole electrodes the lack of good optimization systems makes it difficult to take full advantage of the four electrodes available on the left side.
It has been observed that the origin of the pace pulse has large impact on the cardiac performance, this is inter alia due to the fact that scar and/or ischemic tissue may serve as an obstacle for the depolarization wave on its propagation through the heart tissue.
The inventors have realized that this causes the wave front to move much slower and/or is forced to make a detour around the obstacle resulting in a less than optimal heart beat. However, by pacing from a slightly different location the propagation of the depolarization wave may be facilitated and thus improving heart performance. E.g. a quad pole lead offers the possibility to improve the heart performance by selecting which of the four electrodes to pace from. However, so far, no or only limited possibilities are available to guide the physician in the electrode selection during implantation and follow-up as well as when the patient is out of the hospital (automatic optimization).
Thus, the general object of the present invention is to achieve a heart stimulating device adapted to optimize hemodynamic performance of the heart by analysing and monitoring different electrode selections, e.g. for selecting an optimal electrode configuration.